Portable electronic devices, such as mobile telephones, personal digital assistants, laptop computers, tablet computers, global positioning system receivers, portable games, radios, cameras and camera accessories, and the like are becoming increasingly widely used globally. The portable electronic device industry and their suppliers are increasingly concerned about the environmental footprint, greenhouse gas emissions and depletion of natural resources. Therefore it is increasingly desirable or necessary to use materials derived from renewable resources and having overall low negative environmental impact.
Portable electronic device covers are a particularly demanding materials application. They provide protection of internal components from impact and from contamination. It is thus important that the materials used for portable electronic device covers have high impact resistance. The poly(lactic acid) (PLA) is a polymer derived from renewable resources used in limited cases in portable electronic device covers. But PLA has low mechanical properties and is not widely used.
Additionally, hand held electronic devices such as mobile phones often have antenna inside of housing protected by cover. For optimal functioning of a mobile telephones it is often necessary for the cover be as transparent as possible to electromagnetic radiation having frequencies in the range of about to 40 MHz to 6 GHz and that the material's response to such electromagnetic radiation not vary significantly as a result of environment conditions such as temperature and relative humidity. Otherwise, the amplitude of the radio signals sent and received by the telephone can be affected, resulting in a lost or weakened connection or requiring increased power consumption to maintain a signal at a desirable level. Polycarbonate/acrylonitrile-butadiene-styrene (ABS) has good radio transparency and good impact resistance, and has been a standard material for mobile phones covers. However it does not contain any renewable content.
Thermoplastic polyamide compositions are desirable for use in making mobile telephone covers because they exhibit good physical properties and are conveniently and flexibly molded into a variety of articles of varying degrees of complexity and intricacy. However, many polyamides absorb significant amounts of moisture when exposed to atmospheric conditions, which may decrease the transparency of the compositions to 40 MHz to 6 GHz electromagnetic radiation. Typically, the greater the level of moisture absorbed by the composition, the less transparent the composition is to 40 MHz to 6 GHz electromagnetic radiation. Polyamide 12, for example, has good resistance to moisture absorption, but it typically does not contain any renewable carbon content. Polyamide 11 is derived from renewable resources and has low moisture absorption but exhibits low tensile modulus. Thus, when used in covers does not provide sufficient mechanical protection.
Another important attribute of hand held electronic device covers is that they be readily painted. Polyamide 11 and Polyamide 12 are very difficult to paint.
Thus there is a need for hand held electronic covers that includes a polyamide composition, being partially or entirely derived from renewable resources; and also having a combination of good mechanical properties, low moisture absorption and paintability.